Method and apparatus for communicating through a region of ionized gas



May 12, 1964 P. MoLMUD METHOD AND APPARATUS FOR COMMUNICATING THROUGH A REGION 0F IONIZED GAS Filed Oct. 4. 1960 INVENTOR. 10AM Mal/Ma ff/f 177' THF/Vf )51 Technology Laboratories, Inc., Los Angeles, Calif., Aa

. corporation of Delaware A Filed Oct. 4, 1960, Ser. No. 60,448

5 Claims. (Cl. S25- 65) This invention relates to radio wave communication and, more particularly, is concerned with improved methods and apparatus for establishing such communication through a region of ionized gas which attenuates radio waves.

In modern times, there is an increasing number of practical situations where attenuating regions of ionized gases lie adjacent one of two stations between which radio communication is desired. Sometimes the ionized gases include water vapor as a substantial constituent. For example, communication between a ground station and a rocket missile while the rocket is ring is complicated by the presence of an intervening region of ionized rocket exhaust gases. While -it is possible to `avoid radio propagation through the rocket exhaust gases by placing transmitters downrange of the trajectory of the missi1e, it is desirable to be able to communicate with the missile from a point near its launching site, in which case communication must be through the exhaust region.

The present invention is based 0n the recognition that an increase in the electron energy of an ionized medium may under certain limiting conditions result in decreased attenuation of radio communication signals. For example, an increase in the energy of the electrons 1n an ionized gas may result in a decrease in the colhsion frequency of the electrons within certain ranges of electron energy, and hence a decrease in the attentuating effect of the ionized gas when the frequency of the radio signal is greater than the electron collision frequency.

This property obtains when the ionized gas includes substantial quantities of certain constituents, for example Water vapor. In general, constituent gases whose molecules have permanent electrical dipole moments can be expected to demonstrate the property of reduced electron collision frequency with increased electron energy; for example, ammonia, the halogen acids', nitric oxide, nitrogen dioxide, phosphine, potassium chloride, sulphur dioxide, formaldehyde, hydrogen cyanide, nitro methane, nitro benzene, and many others. At the present time, the presence of water vapor rather than the Vother gases mentioned yaccounts for 'the important practical situations, such as in rocket exhaust where Water vapor appears in substantial quantity as one of the products of combustion.

Furthermore, many solid propellant rockets will contain substantial amount of gaseous hydrochloric acid as a constituent of their exhaust product. Hydrochloric acid-will possess the important characteristics which are possessed by Water vapor, and are taken advantage of in this application.

In communicating radio waves between iirst and second stations, adjacent the first of which is a region of ionized gas having the property that increased electron energy results in decreased attenuation, the method of the present invention incorporates the steps of directing a rst radio signal from the first station along a path toward the second station through the ionized region at a frequency and power level suicient to significantly increase the energy level of the electrons in the ionized gas along the path, and simultaneously communicating a second radio signal containing intelligence between the stations along this path.

United States Patent() er' l ice By the present invention, as typically applied to the launching of a rocket missile, a powerful radio signal is transmitted from the missile with its energy focused along a beam in the direction of a ground station. This powerful signal alters the characteristics of the rocket exhaust trail for a significant distance by heating the electrons and thus lowering their collision frequency. A relatively weak communication signal from the ground now encounters an ionized medium Whose electrons have a lower collision frequency and, therefore, the weak sigual is ableto pass through the ionized medium with substantially less attenuation..

For a more complete understanding of the invention, reference should be made to the accompanying drawing, wherein:

FIG. 1 is a pictorial representation of a missile leaving its launching area and showing the normal path of u the regionof the exhaust gases, indicated generally at 16. These exhaust gases typically for hydrocarbon-liquid oxygen propellants include a high percentage of water Vapor as well as carbon dioxide and other constituents of rocket exhaust. In the absence of the arrangement of the present invention, because ,of high attenuation of the radio signal in passing through the exhaust region,

radio communication is unreliable until the vehicle has altered its orientation to permit the radio signal to avoid the region of the exhaust gases.

As shown in FIG. 2, the vehicle 12 includes a radio receiver 18 coupled to an'antenna 20. The vehicle 12 may also be provided with a low power communication transmitter 22, which may utilize the same antenna 20.

In accordance with the present invention, the vehicle 12 is provided with a high power transmitter 24 which may provide either a C.W. output signal or ay pulsed output signal from a transmitting antennay 26. A pulse source 28 is shown for providing a pulsed output of the transmitter 24. The antenna 26 may preferably be a directional antenna for directing the radio signal from the transmitter 24 in a beam along a path back towards the ground station 14. The antenna 26 may be controlled to home on the ground station by an .antenna positioning control mechanism 30 which derives -its control signal from the receiver 18. The manner in which a directional antenna is made to home on a distant transmitting station is well known and forms no part of the present invention.

It can be shown that the attenuation of a radio Wave in passing through an ionized medium is a function of the Wave frequency, the electron density in the ionized medium, and the collision frequency between electrons and the gas molecules. In particular, attenuation per unit length of a relatively weak radio signal, i.e., a signal of such a low energy level that it does not materially increase the electron energy in the ionized region, varies linearly with electron collision frequency in a region of weakly ionized water vapor when wave frequency is greater than collision frequency. In an atmosphere high in Water vapor content, such as the eX- haust region of a rocket engine, for example, the electron collision frequency has been found to vary inversely mitter 24 is beamed by the antenna 26 back towards thev ground station 14. The strong signal increases the energy f of the electrons in the exhaust region. This increase'of electron energy results in a decrease in the attenuation of the weak radio signals providing communication between the ground station 14 and the vehicle 12.

There are several limiting factors which must be taken into consideration as regards the strong signal. As a general rule, the higher its frequency, the better penetration is provided. However, the higher the frequency, the more power is required to raise electron energies by the same factor. The energy of the high power signal must be suiciently large at whatever frequency is selected in order to provide the necessary-penetration of the ionized region and to raise the energy of the velectron sufciently to provide a significant reduction in the attenuation of the weak signal. At the same time, the power level must not be so high as to signicantly increase the amount of ionization of the exhaust region. For example, a signal of the order of 1100 megacycles has a sufficiently low attenuation to provide good penetration of the exhaust region. At the same time the signal power required to raise the energy level of the electrons in the exhaust region is not too high for satisfactory operation. Successful utilization of the invention is not, however, limited to this one frequency. The weak Vsignal should have a frequency higher than the collision frequency of the electrons in the absence of the strong signal.

The average signal power requirement can be reduced by pulsing the high power transmitter.V It is necessary that the pulse length be substantially longer than the relaxation time for the electrons where the relaxation time is defined v being the collision frequency and A being the average fractional energy loss suffered by an electron on collision. For example, a pulse length of the order of -7 sec. is sufficiently long.

While the invention has particular application to improving transmission of weak radio signals through rocket exhaust, it may be applied to transmission through other ionized regions wherein an increase in electron energy is accompanied by a decrease in attenuation of radio signals.

I claim: Y

1. In communicating radio waves between firstv and second stations, adjacent the first of which is a region of ionized gas having the property that increased electron energy results in decreased attenuation, the method comprising the steps of directing a first radio signal from the first station along a path toward the second station through the ionized region at a frequency and power level sufficient to significantly increase the electron energy of the ionized gases along said path, and simultaneously communicating a second radio signal containing intelligence between the stations along said path.

2. The method of claim 1 wherein the first radio signal is pulsed, the pulse duration being longer than the relaxation time of the electrons in the ionized gas region along said path.

3. In communicating radio waves between first and second stations, adjacent the rst of which is a region of ionized gas having the property that increased electron energy results in decreased attenuation, the method comprising the steps of directing a first radio signal from the first station along a path toward the second station through the ionized region at a frequency and power level suicient to significantly increase the electron energy of the ionized gases along said path, and simultaneously Ycommunicating a second radio signal containing intelligence between the stations along said path, the second radio signal having a frequency higher than the electron collision frequency in the ionized gases along said path.

4. In a communication Vsystem for communicating radio waves through an adjacent region of ionized gas having the propertyv that increased electron energy results in decreased attenuation, the combination which comprises a power transmitter for directing energy along a path through the ionized gas region at a frequency and power level sufficient to significantly increase the electron energy in the ionized gas region along said path, and a cooperating communication transmitter for simultaneously transmitting intelligence signals along said path.

5. In a communications system for providing communication with a rocket vehicle from the groundthrough the ionized exhaust gases, the combination comprising a ground transmitter for directing radio communication signals to the vehicle, a receiver on the vehicle for receiving the radio communication signals, and a high power transmitter on the vehicle for directing a radio signal toward the ground transmitter, the high power vehicle transmitter producing a signal below the energy Vlevel at which increased ionization of the exhaust gases is produced by the radio signal but above the energy level and at a frequency which will penetrate through the region of the ionized exhaust gases, whereby the electron energy of the ionized exhaust gases is increased along the communication path between the ground transmitter and the vehicle receiver, the ground transmitter operating at a carrier frequency above the collision frequency of the electrons in the exhaust gases in the presence of the strong signal from the vehicle transmitter.

References Cited in the file of this patent Busignies Ian. 27, 1959 

1. IN COMMUNICATING RADIO WAVES BETWEEN FIRST AND SECOND STATIONS, ADJACENT THE FIRST OF WHICH IS A REGION OF IONIZED GAS HAVING THE PROPERTY THAT INCREASED ELECTRON ENERGY RESULTS IN DECREASED ATTENUATION, THE METHOD COMPRISING THE STEPS OF DIRECTING A FIRST RATIO SIGNAL FROM THE FIRST STATION ALONG A PATH TOWARD THE SECOND STATION THROUGH THE IONIZED REGION AT A FREQUENCY AND POWER LEVEL SUFFICIENT TO SIGNIFICANTLY INCREASE THE ELECTRON ENERGY OF THE IONIZED GASES ALONG SAID PATH, AND SIMULTANEOUSLY 